Apparatus for diluting an acetic acid solution of cellulose acetate with water



Jan. 30, 1968 JORI 3,366,458

APPARATUS FOR DILUTING AN ACETIC ACID SOLUTION OF CELLULOSE ACETATE WITHWATER Original Filed June 5, 1963 INVENTOR LUCIANO JORI ATTORNEYS3,366,458 APPARATUS FOR DILUTlNG AN A'CETIC ACID SOLUTION OF CELLULOSEACETATE WITH WATER Luciano Jori, 4 Via Freguglia, Milan, Italy Originalapplication June 3, 1963, Ser. No. 285,092, now Patent No. 3,332,937,dated July 25, 1967. Divided and this application Jan. 18, 1967, Ser.No. 610,179

Claims priority, application Italy, June 22, 1962, 12,505/ 62 1 Claim.(Cl. 23267) ABSTRACT OF THE DISCLOSURE The invention relates to anapparatus which is useful in achieving the water dilution of an aceticacid solution of cellulose acetate with a Water solution of acetic acid.The apparatus comprises an inclined wall along which flows the aceticacid solution of cellulose acetate which is to be diluted. An atomizeris present through which an aqueous solution of acetic acid isintroduced into the apparatus. The atomized aqueous solution of aceticacid contacts the acetic acid solution of cellulose acetate as it flowsalong the inclined wall and dilutes the same. The apparatus containsmeans for introducing the solution to be diluted into the apparatus,means for removing the diluted solution and means for recirculating theacetic acid solution of cellulose acetate.

This application is a division of US. patent application Ser. No.285,092, filed June 3, 1963, now Patent 3,332,937.

The object of the present invention is to provide an apparatus fordiluting an acetic acid solution of cellulose acetate with water.

As in the case of other batch processes, also in the production ofcellulose acetate it has been attempted to transform the batch processinto a continuous process. One of the biggest difliculties to beovercome, however, is that encountered at the moment of theprecipitation of the cellulose acetate from its acetic acid solution.

It is known that the acetylation process consists of an esterificationof the cellulose, said esterification being effected after a preliminarytreatment, by acetic anhydride in the presence of acetic acid assolvent, said acetylation occurring in homogeneous phase and in thepresence of a catalyst, normally sulphuric acid. Under these conditions,the cellulose triacetate forms which, however, does not serve thepurpose for certain applications. Thus, for instance, this compound isuseless for the production of textile fibers from acetonic solutions,and is useless generally for the preparation of solutions in acetone,and is also useless for certain uses as plastic material. For theseuses, the acetylation degree is too high, and must be reduced untilobtaining a product having an acetyl number about 54. This will beobtained by submitting the triacetate, even in acetic acid solution, toan hydrolysis, or to a saponification. After this operation has beencarried out up to the desired limit, the cellulose acetate will beprecipitated from its acetic solution and this is done by pouring theacetic acid solution itself into water.

This operation shows certain difliculties also in the batch process;these difiiculties are remarkably increased when the batch process is tobe transformed into a continuous process. The precipitated celluloseacetate is submitted to a thorough washing in order to remove all theacetic acid contained therein. However, often in the precipitationcrumbs of product will be formed, having a horny aspect which cannot bewell washed. In the batch process, in these instances, the duration ofwashing is extended, but in the continuous process, of course, this isnot pos- 3,355,458 Patented J an. 30, 1968 sible, as the durations totime are tied to the other operations.

It is known that the precipitation of the cellulose acetate from itsacetic acid solution is rendered easier, even effecting saidprecipitation by pouring it into water, if before this operation acertain amount of water is added to the acetic acid solution, preferablyin the form of a diluted acetic acid solution, so as to bring thesolubility of the cellulose acetate to its limit, however avoiding aprecipitation thereof even in minimum amounts. By effecting theprecipitation of the acetate from a solution to which water has beenadded as aforedescribed, regular grains of cellulose acetate will beobtained, free from particles having a horny aspect, and also free fromunduly small particles, having a powder aspect, also said particlesbeing difiicultly washable.

It will be suitable to add the water to the acetic acid solution ofcellulose acetate, under the form of a low concentration acetic acidwater solution. Thus for instance for an acetic acid solution of acellulose acetate soluble in acetone, having an acetyl number about 54.5and a Baum viscosity about 45, it will be convenient to use an 8-10%acetic acid water solution.

From a 12% cellulose acetate solution it will be possible, whenoperating under given conditions, to reduce the acetic acid contents to53-54%.

This dilution can be effected, however, under particular conditionswithout incurring the formation of acetate crumbs or separation ofacetate powder which, as aforesaid, hinder a good washing of thecellulose acetate after its precipitation.

It has now been found, and this is the object of the present invention,that this dilution can be efiected in the best way by using theapparatus as described later on, wherein the cellulose acetate aceticacid solution flows in a relatively thin layer along an inclined andpreferably frustoconical wall. While the cellulose acetate solutionmoves along this wall, said solution will contact the acetic aciddiluted solution which will have been previously atomized. This occurswithin a reservoir, into which enters continuously the cellulose acetatesolution to be diluted and the diluted acetic acid solution, andwherefrom also continuously outflows the diluted cellulose acetatesolution. The cellulose acetate solution preferably circulates inendless circuit with a speed remarkably higher than the feeding rate.

The layer of the cellulose acetate acetic acid solution flowing on thefrustoconical wall will be 5-15 millimeters thick, preferably 8-10millimeters thick.

For a better knowledge, the process and the apparatus will behereinafter described with reference to the attached drawing.

In the drawing, the reference numeral 1 denotes a tank having a greaterdiameter at its top portion, and tapered downwards so as to originatethe frustoconical wall 3. Inside the tank, a second frustoconical wall 2is provided, the lower portion of which is close to the wall 3 so as tocreate a circular slot a few millimeters wide, so that the celluloseacetate solution entering into the top portion of the tank 1 through theinlet 6 is carried to flow on the wall 3, under the wall 2 in a thinlayer. Through the atomizer 11 acetic acid diluted solution enters intothe tank. The atomized diluted acetic acid solution strikes thecellulose acetate solution while the latter flows downwards along thewall 3. This solution collects in the bottom portion of the tank 1,wherefrom it will be extracted through the coupling tube 4 by means ofthe pump 5 carrying the solution into the tank 1 through the inlet 6.Into the tank 1 is continuously fed the cellulose acetate solution to bediluted through the inlet 7, and through the outlet 8 and by means ofthe pump 9, the corresponding amount of diluted solution is continuouslyremoved. At the bottom of the apparatus there is provided an opening 10for cleaning.

Within the tank 1 is always maintained a liquid level above the twofittings 7 and 8 and said level is ensured by the level of a feedingtank (not shown in the figure) wherefrom tank 1 is fed through thefitting 7.

Hereinafter by way of non-limitative example, a practical embodiment ofthis invention will be described.

EXAMPLE The dilution apparatus as above described is fed, with 4,000kilograms per hour of an acetic acid solution of cellulose acetatecontaining 12% cellulose acetate and 65.4% acetic acid, the balancebeing water and impurities coming from the cellulose acetylationprocess. The cellulose acetate has an acetyl number 54, and a Baumviscosity 44. Through the atomizer, 1,080 kilograms per hour of watersolution of 8% acetic acid are introduced into the same apparatus. Thesolution of cellulose acetate is recycled into the dilution apparatus ata rate of 120 cubic meters per hour. From the apparatus are extracted5,080 kilograms per hour of perfectly limpid diluted solution of acetateof cellulose, containing 9.45% of cellulose acetate and 53.20% aceticacid.

When this solution is poured into Water, by the technical known means,an easily washable product is obtained, free from horny crumbs andpowder.

The present invention has been described in one preferred embodiment, itbeing however, understood that variations might be practically adoptedwithout departing from the scope of the present invention.

Having thus disclosed the invention, What is claimed is:

1. An apparatus useful in achieving the water dilution of an acetic acidsolution of cellulose acetate with a water solution of acetic acid whichapparatus comprises:

(1) a substantially cylindrical tank having a top portion of greaterdiameter than the lower portion, said tip and lower portions beinginterconnected by a first frustoconical surface;

(2) means for atomizing an aqueous solution of acetic acid and directingsaid atomized solution into contact with the said frustoconical surface;

(3) a second frustoconical surface tapering upwardly within the firstfrustoconical surface and encircling the atomizing means, the lowerextremity of the second conical surface being spaced from the firstconical surface by a few millimeters;

(4) means for introducing the acetic acid solution of cellulose acetateinto the said top portion of the tank;

(5) outlet means in the lower portion of said tank for withdrawing thediluted solution; and

(6) means for recirculating the acetic acid solutions of celluloseacetate, and comprising an outlet in the lower portion of the tank fromwhich the solution is Withdrawn and pumping means for delivering thewithdrawn solution to the inlet means above the frustoconical surface.

References Cited UNITED STATES PATENTS 2,575,119 11/1951 Peebles 159-42,640,761 6/ 1953 Wiseman 15913 2,969,347 1/1961 Bellinger 159162,974,131 3/1961 McLeod 23-275 X NORMAN YUDKOFF, Primary Examiner.

WILBUR L. BASCOMB, IR., Examiner.

S. EMERY, Assistant Examiner.

